Fig. 131.—Cross-Section of Peekskill Tunnel, Showing Lining.
The side wall foundation trenches were first excavated from 1 to 3 ft. deep and footing concreted and leveled up, the back of the footing being carried up against the rock and the front lined to forms giving a 12-in. offset to the side wall. The footings contained 200 cu. yds. of concrete. Platforms 25 ft. square and level with the springing lines were then erected at each end of the tunnel. A derrick was placed at each platform to handle skips between it and the material tracks which ran underneath and through the tunnel with a turnout at each end for switching back empty cars. A 60 H.P. portable boiler supplied steam for the derrick engines and a pump. The wall forms were built and erected in panels 12 ft. long; these panels had 4×6-in. plates and sills, 4×4-in. studs 3 ft. on centers and 2-in. dressed and matched spruce sheeting. Four panels were set up, two on each side, midway of the tunnel and braced to the tunnel track. Wheelbarrow runways carried on bents were built from the platforms to the forms, one from one platform to one side, another from the other platform to the opposite side. Temporary bulkheads were erected to close the ends of the forms and they were filled. Meanwhile carpenters were setting other panels at each end of the two first erected on each side. After 24 hours the panels first set were taken down and moved ahead and the processes described continued until the full length of side wall was completed. The side walls were not concreted back to the rock; back forms of 1-in. hemlock were used and the space remaining was filled with spalls. The side walls contained 692 cu. yds. of concrete.
Arch forms were erected for 96 ft. at the center of the tunnel, using 12-ft. lagging, so that sections of this length could be taken down and moved ahead, nine at each end. The lagging was first laid to a height of 3 ft. above the springing line on each side and the concrete dumped directly in place from runways laid on the lower chords of the arch ribs, which were placed 4 ft. apart. When the concrete reached a height too great for direct discharge into the forms it was dumped on the runway and passed over with shovels. On the upper portion of the ring the concrete was first shoveled to a platform erected on the center posts of the ribs about 2 ft. below the crown and then passed in on the lagging which was laid in 4-ft. instead of 12-ft. lengths at this stage of the work. As soon as each section of arch ring was completed it was waterproofed with six layers of tar paper laid in hot tar and then packed behind with spalls. The arch centers were struck in a comparatively short time; in one instance they were struck 90 hours after the last concrete was placed and no settlement was apparent. The arch forms stuck so fast to the concrete, however, that they had to be jacked down by chiseling out the lagging so as to get a bearing on the arch concrete and by nailing thrust blocks to the rib posts. The section was then hauled ahead by passing the main fall of the derrick through a snatch block on the first rib. When hauled clear of the lining all but the first 3-ft. of lagging on each side was removed; they were then jacked into position. The arch ring contained 932 cu. yds. of concrete.
Including the portal head walls 1,948 cu. yds. of concrete were laid at the following costs for labor and materials:
| Item. | Total. | Per cu. yd. |
| Cement at $1.63 per bbl. | $ 5,755.50 | $2.951 |
| Sand at $0.75 per cu. yd. | 662.94 | 0.339 |
| Stone at $0.80 per cu. yd. | 1,303.20 | 0.668 |
| Lumber— | ||
| Mixing platforms and runways | 336.89 | 0.174 |
| Ribs, including hand sawing | 234.10 | 0.120 |
| Backing boards | 134.44 | 0.069 |
| Lagging | 341.04 | 0.176 |
| Sheathing | 268.49 | 0.137 |
| Plates, sills, studs, braces | 182.75 | 0.093 |
| Coal | 118.73 | 0.061 |
| Oil | 16.12 | 0.008 |
| Hardware, nails, spikes, etc. | 224.39 | 0.118 |
| Tools | 181.10 | 0.093 |
| Freight on stone, cement, etc. | 3,089.86 | 1.584 |
| Labor of all kinds | 8,036.31 | 4.121 |
| ————— | ——— | |
| Total | $20,885.86 | $10.712 |
METHOD OF LINING CASCADE TUNNEL, GREAT NORTHERN RY.—The Cascade Tunnel, 13,813 ft. long, built in 1897-1900, was lined throughout with concrete from 24 ins. to 3½ ft. thick, mixed and placed in the following manner: It was necessary to place the lining without interfering with the transportation of materials and excavated material to and from the work ahead. The arrangement adopted to secure this end is shown by Fig. 132. A platform 500 ft. long was constructed at the elevation of the wall plates; the rear end of this platform was reached by an incline, up which the cars loaded with concrete were hauled by an air hoist and cable and delivered to any point on this platform. While each 500 ft. of tunnel was being concreted, the next 500 ft. of platform in advance was being built, with its approach incline, so that there was no delay in the work.
Complete concrete plants were installed at each portal, advantage being taken of the side hills of the approach into the mountain to handle as much material as possible by gravity. Each plant was equipped with a No. 6 Gates crusher, 40-in.×8-ft. rock screens, and 16-in.×16-ft. screw concrete mixers. Large storage bins for the cement, sand and stone were built adjacent to the mixer plant. A 1-3-5 concrete was used. The stone was crushed from the best rock obtained in the tunnel excavation. This rock was loaded into the regular muck cars, taken to the portal by electric motors, and then dumped into other cars below the level of the muck cars. These cars were hauled by hoisting engine and cable to the crusher floor and then dumped and sorted to avoid danger from pieces of unexploded dynamite. It was then run through the crushers, washers and screens to the stone bin and thence to the mixers. The mixed concrete was discharged into cars on the level of the muck car tracks and these cars were taken by motor into the tunnel to the incline, up which they were hauled by cable and dumped on the platform. From the platform the concrete was shoveled into the wall forms or onto the centers as desired.
Fig. 132.—Traveling Platform Used in Lining Cascade Tunnel.
The walls were concreted in alternate 12-ft. sections, the weight on the timber arch thus being gradually transferred from the plumb posts to the walls. The roof arch was also built in 12-ft. sections, the centers being in sections of corresponding length which were moved forward on dollies and jacked up as the work advanced. Ten sections of centering were used at each end. An average of 7 bbls. of cement were used per lineal foot of lining. The average monthly progress of lining was about 600 ft. at each end. The concrete lining cost $44 per lin. ft. of tunnel, done by company forces.